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Cummins Cold Starting/Diagnosis

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I saw a lot of threads about this on other forums and people didn't know how it should be starting in the winter, what to check if it doesn't start right, etc. In the summer the engine compresses the air and it doesn't take much to make summer air hot enough to ignite the fuel. The cylinder walls and pistons are cold when you first start it and any heat from compression is absorbed through them. In the summer this isn't a concern since the rate of absorption is much less with things that are already hot. In the winter, the engine block will be whatever the ambient is. The colder it is the more it will take to get it started because the cylinder walls and piston are so cold that they easily absorb any heat from compression. To counter this issue, diesels have grid heaters or glow plugs. Glow plugs are inside the combustion chamber in about the same spot as where a spark plug would go on a gas engine. They glow red when they are on and try to heat the combustion chamber up. The grid heaters do the same thing but in a different manner. They are placed inside the intake horn and heat the incoming air up to be sucked into the combustion chamber. Both forms of combustion chamber heating are there for the same purpose, to heat the air up hot enough that it counteracts the cooling effect of the cylinder walls and pistons. By making the air hot, the heat of compression makes it even hotter and even with the walls and pistons will rob some heat, it stands a much better chance of starting than if it had no intake heater at all. Typical engine starts with the grid heater should be 1-2 cranks all the way down to 0F. I would say you could start at 1 crank with it brand new and give it 1 crank more for every 100k miles. So at 100k, 2 cranks is what it should take to start at 0F. At 200k, 3 cranks. 300k, 4 cranks.. That is just a rough estimate of what it should take to start it, every truck is different and depending on how they were cared for they may take a little longer to start. If you take care of your truck, it may hardly wear and you will not have to crank much more for every 100k you put it on it. My truck had 250k when I got it and there was a time when it would start without the grid heaters at 0F in half a crank with no smoke at all. So it is very possible to keep the compression good enough to accomplish that, but it is not recommended to skip the grids just to "see if it will start" as it is hard on it and will deteriorate compression over time from doing that. If the engine takes more than 10 cranks to start, something is probably wrong. The grid heaters may not be working which you can read up on them here: Grid Heaters Another possible cause is poor cranking speed which can be from a bad connection to the battery, bad batteries (or batteries that don't have a high enough cranking amp rating), a bad starter or bad starter contacts. More info on Voltage Drop (poor connections) / Starter / Starter Contacts. Fuel gelling can also be a possible cause. This shouldn't be a concern if your state experiences cold weather as the diesel stations should be putting in antigel, but sometimes even then there is an unexpected cold spell that may gel the fuel. If the truck starts then dies and you think it is gelled, check the fuel filter as it is probably clogged since gelled fuel will not flow through it. On 12 valves, timing can be a concern. It can slip and once it gets too far advanced or retarded, it will become very hard to start in the cold. Timing Info Oil can also be something of concern as too thick of oil may keep the truck from cranking over fast enough. Conventional (non-synthetic) oil has a pour point of around -20F, which means it can be used down to that point. Synthetic oil is around -40F. Conventional will be fine down to 0F. If you happen to live where the temps are consistently under 0F, you should consider synthetic to allow it to crank over easier and get oil pressure faster. Those are the causes of cold start issues. Don't forget about common start issues (any temp) that can also be the cluprit, such as air in the fuel lines. If you have a 24V, check for codes and look them up in the /forums/97-24-Valve-Error-Code-Shop">code section, ask questions if you still need help.

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Bigger injectors can and will cause it to start a bit harder as it gets colder also. My 02 with the 150 bd injectors is not a happy camper if its under 10*F and not plugged in, I some times have to try it a couple 3 times and crank for a while and multiple grid heats to get it to fire up and run. When it had smaller injectors in it wasn't an issue.

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Way back, I had a very well used '83 Ford Ranger (only built 83-4) with a 2.2 natural diesel (Mazda built Perkins)... my friend's S10 would just walk away from me. Over the summer it lost all but 1 glow plug... when winter came, I had to go search out new GPs. Darn tuff to start on one cylinder. The transmission came loose from the bellhousing & cracked the case... it wasn't worth fixing.BTW, what triggers our grid heaters? IAT or some other senser?

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Way back, I had a very well used '83 Ford Ranger (only built 83-4) with a 2.2 natural diesel (Mazda built Perkins)... my friend's S10 would just walk away from me. Over the summer it lost all but 1 glow plug... when winter came, I had to go search out new GPs. Darn tuff to start on one cylinder. The transmission came loose from the bellhousing & cracked the case... it wasn't worth fixing. BTW, what triggers our grid heaters? IAT or some other senser?

Mike found out that they are triggered by the ECT and IAT before the engine is running. Don't know if he tested for post starting. I noticed my 12V will default to 30 seconds if I unplug the IAT and it will just blink after the engine starts.

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It's weird... Sometime there is grid heaters and other times there isn't... :shrug: Like bone cold start of 25*F ECT and 132*F IAT there is no pre-heat grid because the wait to start goes off quick and no grid relay click. now starts roughly a bit of idling and smoothes right out. Still no post grid heat. Now I ran to town the other day and came back left the truck sit outside and it cooled a bit 120*F ECT and still the 132*F and when I started it the grid heaters started to cycle... Hua? :stuned: So now I'm stumped... :shrug:

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